118 CARBONIFEROUS LAMELLIBRANCHIATA. 



It is also very difficult to ascertain the side to which the valve belongs. I 

 think, however, that the anterior ear is narrower and longer, and is a little better 

 defined from the rest of the valve than the posterior ear. 



Syxcyolonema sowekbyj, M'Coy, sp., 184-1. Plate XVIII, figs. 21 — 26. 



Peoten Soweebii, M'Coy, 1844. Synops. Carb. Foss. Ireland, p. 100, pi. xiv, fig. 1. 



— - Valdaicus, de Vernetiil, 1845. Murchison's Geol. Russia, vol. ii, p. 328, 



pi. xxvii, fig. 9. 



— Sowebbii, Morris, 1854. Cat. Brit. Foss., 2nd edit., p. 175. 

 Amusium Sowebbii, M'Coy, 1855. Brit. Pal. Foss., p. 478. 

 Aviculopecten Sowebbii, Armstrong and Young, 1871. Trans. Geol. Soc. Grlasg., 



vol. iii, App., p. 47. 

 Entolium aviculatum, Hayden, 1872. Rep. U. S. Geol. Surv., p. 189, pi. ix, 



figs. 11 a.— 11 g. 

 Pecten (Pseudamusium) Bathus, de Koninck, 1873. Rech. Anim. Foss. Carb. 



Bleiberg, p. 94, pi. iii, fig. 19. 

 Sowebbii, Ii. Etheridge, Jan., 1874. Geol. Mag., dec. ii, vol. i, p. 300, 



pi. xiii, figs. 1, 2. 

 — Baity, 1875. Figs. Cliar. Brit. Foss., p. 113, pi. xxxix, fig. 3. 



— ■ (Amusium ?) Sowebbii, E. Etheridge, jun., 1877. Geol. Mag., dec. ii, 



vol. iv, p. 241, pi. xii, figs. 1 — 3. 

 Entolium Sowebbii, B. Etheridge, jun., 1878. Ann. Mag. Nat. Hist., ser. 5, vol. ii, 



p. 30, pi. i, figs. 4, 5. 

 Non — de Koninck, 1885. Ann. Mus. Roy. d'Hist. Nat. Belg., 



torn, xi, p. 241, pi. xxxiii, figs. 5, 6. 



Specific Characters. — Shell below medium size, ovato-elliptical or suborbicular, 

 almost equivalve, and equilateral. The valve formed of a central, pear-shaped, 

 convex portion, bounded in front and behind by an oblique groove, which separates 

 broad, flange-like, flattened lobes. The margin of the valve convexly curved for 

 the greater part of its extent, but near the upper part of the valve both in front 

 and behind, becoming suddenly bent towards the middle line of the valve at a 

 bluntly obtuse angle, then passing upwards and inwards till it meets the ear. The 

 cars are small, triangular, the anterior somewhat better demarcated from the body 

 of the valve than the posterior ear. Ears continuous with the hinge-line, with a 

 st i a ight upper margin in the right valve, but the anterior ear raised in the left 

 valve so that its antero-superior angle is elevated, and the upper border of the valve 

 is formed by two lines, which are inclined at an angle. The mnbones small, 

 flattened, triangular, and pointed, central. 



Interior. — The internal surface is smooth. The adductor muscle-scar is shallow 

 and round, placed high up in the valve and posterior to the middle line. The 



